A tremendous variety of devices used today rely on actuators of one sort or another to convert electrical energy to mechanical energy. The actuators “give life” to these products, putting them in motion. Conversely, many power generation applications operate by converting mechanical action into electrical energy. Employed to harvest mechanical energy in this fashion, the same type of actuator may be referred to as a generator. Likewise, when the structure is employed to convert physical stimulus such as vibration or pressure into an electrical signal for measurement purposes, it may be referred to as a transducer. Yet, the term “transducer” may be used to generically refer to any of the devices. By any name, a new class of components employing electroactive polymers can be configured to serve these functions.
Especially for actuator and generator applications, a number of design considerations favor the selection and use of advanced electroactive polymer technology based transducers. These considerations include potential force, power density, power conversion/consumption, size, weight, cost, response time, duty cycle, service requirements, environmental impact, etc. Electroactive Polymer Artificial Muscle (EPAM™) technology developed by SRI International and licensee Artificial Muscle, Inc. excels in each of these categories relative to other available technologies. In many applications, EPAM™ technology offers an ideal replacement for piezoelectric, shape-memory alloy (SMA) and electromagnetic (EM) devices such as motors and solenoids.
As an actuator, EPAM™ technology operates by application of a voltage across two thin elastic film electrodes separated by an elastic dielectric polymer, such as silicone or acrylic. When a voltage difference is applied to the electrodes, the oppositely-charged members attract each other producing pressure upon the polymer therebetween. The pressure pulls the electrodes together, causing the dielectric polymer film to become thinner (the z-axis component shrinks) as it expands in the planar directions (the x- and y-axes of the polymer film grow). Another factor drives the thinning and expansion of the polymer film. The like (same) charge distributed across each elastic film electrode causes the conductive particles embedded within the film to repel one another expanding the elastic electrodes and dielectric attached polymer film.
Using this “shape-shifting” technology, Artificial Muscle, Inc. is developing a family of new solid-state devices for use in a wide variety of industrial, medical, consumer, and electronics applications. Current product architectures include: actuators, motors, transducers/sensors, pumps, and generators. Actuators are enabled by the action discussed above. Generators and sensors are enabled by virtue of changing capacitance upon physical deformation of the material.
Artificial Muscle, Inc. has introduced a number of fundamental “turnkey” type devices that can be used as building blocks to replace existing devices. Each of the devices employs a frame structure to support the EPAM™ film whereby application of a voltage shifts the position of the device assembly back and forth. The film can be engaged with (e.g., stretched by) the frame in such a way so as to pre-strain the film. It has been observed that pre-straining improves the dielectric strength of the polymer, thereby offering improvement for conversion between electrical and mechanical energy by allowing higher field potentials.
By varying the frame configuration and the manner in which the EPAM™ material is supported by the frame, different types of actuators can be provided to address many types of applications. Non-limiting examples of actuator types include linear actuators, bending beam actuators, planar actuators, diaphragm actuators, etc.
Linear actuators, often referred to as “spring roll” actuators, are prepared by wrapping layers of EPAM™ material around a helical spring. The EPAM™ material is connected to caps/covers at the ends of the spring to secure its position. The body of the spring supports a radial or circumferential pre-strain on the EPAM™ while lengthwise compression of the spring offers axial pre-strain. Voltage applied causes the film to squeeze down in thickness and relax lengthwise, allowing the spring (hence, the entire device) to expand. By forming electrodes to create two or more individually addressed sections around the circumference, electrically activating one such section causes the roll to extend and the entire structure to bend away from that side.
Bending beam actuators are formed by affixing one or more layers of stretched EPAM™ material along the surface of a beam. As voltage is applied, the EPAM™ material shrinks in thickness and grows in length. The growth in length along one side of the beam causes the beam to bend away from the activated layer(s).
Another class of devices situates one or more film sections in a substantially planar frame structure. In one variation of planar-type actuators, the frame includes closed linkages or spring-hinges. When a linkage frame is employed, a biasing spring may generally be employed to pre-strain the EPAM™ film. A spring-hinge structure may inherently include the requisite biasing. In any case, the application of voltage will alter the frame or linkage configuration, thereby providing the mechanical output desired within the planar directions defined by the frame structure.
Diaphragm actuators are similarly constructed to the above-described planar actuators, but provide mechanical output outside the physical plane of the frame structure. In many embodiments, diaphragm actuators are made by stretching EPAM™ film over an opening in a rigid frame. Diaphragm actuators can displace volume, making them suitable for use as pumps or loudspeakers, etc.
More complex actuators can also be constructed. “Inch-worm” and rotary output type devices are examples of such. Further description and details regarding the above-referenced devices as well as others may be found in the following patents, patent application publications and/or currently unpublished patent applications:                U.S. Pat. No. 7,064,472 Electroactive Polymer Devices for Moving Fluid        U.S. Pat. No. 7,052,594 Devices and Methods for Controlling Fluid Flow Using Elastic Sheet Deflection        U.S. Pat. No. 7,049,732 Electroactive Polymers        U.S. Pat. No. 7,034,432 Electroactive Polymer Generators        U.S. Pat. No. 6,940,221 Electroactive Polymer Transducers and Actuators        U.S. Pat. No. 6,911,764 Energy Efficient Electroactive Polymers and Electroactive Polymer Devices        U.S. Pat. No. 6,891,317 Rolled Electroactive Polymers        U.S. Pat. No. 6,882,086 Variable Stiffness Electroactive Polymer Systems        U.S. Pat. No. 6,876,135 Master/slave Electroactive Polymer Systems        U.S. Pat. No. 6,812,624 Electroactive polymers        U.S. Pat. No. 6,809,462 Electroactive polymer sensors        U.S. Pat. No. 6,806,621 Electroactive polymer rotary motors        U.S. Pat. No. 6,781,284 Electroactive polymer transducers and actuators        U.S. Pat. No. 6,768,246 Biologically powered electroactive polymer generators        U.S. Pat. No. 6,707,236 Non-contact electroactive polymer electrodes        U.S. Pat. No. 6,664,718 Monolithic electroactive polymers        U.S. Pat. No. 6,628,040 Electroactive polymer thermal electric generators        U.S. Pat. No. 6,586,859 Electroactive polymer animated devices        U.S. Pat. No. 6,583,533 Electroactive polymer electrodes        U.S. Pat. No. 6,545,384 Electroactive polymer devices        U.S. Pat. No. 6,543,110 Electroactive polymer fabrication        U.S. Pat. No. 6,376,971 Electroactive polymer electrodes        U.S. Pat. No. 6,343,129 Elastomeric dielectric polymer film sonic actuator        2006/0119225 Electroactive polymer motors        2005/0157893 Surface deformation electroactive polymer transducers        2004/0263028 Electroactive polymers        2004/0217671 Rolled electroactive polymers        2004/0124738 Electroactive polymer thermal electric generators        2004/0046739 Pliable device navigation method and apparatus        2002/0175598 Electroactive polymer rotary clutch motors        2002/0122561 Elastomeric dielectric polymer film sonic actuatorEach of these documents is incorporated herein by reference in its entirety for the purpose of providing background and/or further detail regarding underlying technology and features as may be used in connection with or in combination with the aspects of present invention set forth herein.        
More complex frame structures have also been developed by the assignee hereof with an eye towards producing more practical and versatile actuator structures. In this regard, frustum-shaped diaphragm actuators are ideal. These are formed by providing a centrally disposed “cap” or disc on the electroactive film of a standard diaphragm type-actuator and then displacing the diaphragm/cap in a direction perpendicular to the plane defined by the frame structure. As such, the cap provides a mechanical preloaded element.
The frustum diaphragm structure is highly practical and advantageous for a variety of applications, including but not limited to pumps, valves, camera lens, light reflectors, speaker diaphragms, multi-axis position sensors/joysticks, vibrators, haptic or force feedback control devices, multi-axis actuators, etc. These frustum-type actuators or more thoroughly described in U.S. patent application Ser. Nos. 11/085,798 and 11/085,804, incorporated by reference in their entirety.
Many of the above-described actuators have configurations which involve push-pull inputs and/or outputs which are in-plane and/or out-of-plane in only two-dimensions. However, more complex frame structures can be employed to provide three-dimensional action. One such example is found in U.S. patent application Ser. No. 11/085,798 in which a saddle-shaped actuator is used to produce a three-dimensional output. More particularly, the actuator is coupled to a pair of “wings” to offer a structure having an output which substantially mimics the flapping wings of a flying bird or bat.
Other complex actuator structures involve the coupling together or “stacking” of two or more actuators to provide two-phase output action and/or to amplify the output for use in more robust applications. The actuators of the resulting structure may all have the same configuration (e.g., all have diaphragm structures) or may have configurations different from each other (e.g., diaphragm and spring roll combination). With any configuration, activating opposite sides of the actuator system makes the assembly rigid at a neutral point. So-configured, the actuators act like the opposing bicep and triceps muscles that control movements of the human arm. Alternatively, two actuators arranged in series offers the potential to double the output in a single direction. U.S. patent application Ser. Nos. 11/085,798 and 11/085,804 disclose such “stacked” actuators.
Biasing against the film is employed to insure that the film moves in a desired direction rather than simply wrinkle upon electrode activation that causes the material to expand. Known biasing means include simple positive rate springs (such as a coil spring and leaf springs), EPAM™ film or non-active film set to pull against the biased material, by resilient foam, air pressure or a weight. U.S. patent application Ser. Nos. 11/085,798 and 11/085,804 disclose a number of such arrangements.
While the devices described above provide highly functional examples of EPAM™ technology actuators/transducers, there continues to be an interest in improving high performance EPAM™ actuators/transducers. In particular, it would be advantageous to improve force or stroke, work and, hence, power output without simply employing more electroactive polymer material. The present invention is directed at making such gains by new modes of selectively biasing the actuator film.